Electric arc metal spray guns are well known in the art, for example, as disclosed in U.S. Pat. No. 3,632,952. The ends of two electrically isolated metal wires are melted in an electric arc struck between the wire ends, and the molten metal is atomized by compressed gas, usually air and sprayed to a workpiece to be coated. A pair of tubular electrodes 12, 12' are connected to a source of electric current, and two pairs of wire feed rollers feed the wire through each of the electrodes. (Figure numbers and reference numerals indicated herein under Background of the Invention refer to figures in the corresponding patent being referenced herein.) An air tube 14 acting as a nozzle is positioned adjacent to the ends of the electrodes 12, 12' and connected to a source of compressed air. The ends of the electrodes are fixedly secured relative to each other and to the air jet nozzle to ensure proper contact of the wires for arc formation and uniform atomization of the molten metal. In the gun device of the above-named patent a portion of the air supplied to the gun is diverted from the main stream to provide a secondary air flow in addition to the primary flow of atomizing air. A chamber 8 formed by the gun housing 4 surrounds the electrodes 12, 12' and the air jet nozzle tube 14. The chamber has a spray opening 21' and is adapted to feed the secondary air in the form of an annular stream of air about the electrodes and air jet nozzle which flows out through the spray opening, resulting in control of the spray pattern and of fineness of the molten metal.
U.S. Pat. No. 4,095,081 discloses an arc spray gun having a head 16 (FIG. 2) of electrically insulating material with two guide passages 22 therein such that the sidewalls of the passages consist of the insulating material. A contact tube 32 for connecting the wires to a source of electric current is provided at a location prior to entry of the wires into the insulated guide passages in the head. The contact tube comprises a pressure pad 36 spring-urged radially through a slot in the contact tube by a spring arm 38.
There also is provided, in the device of the aforementioned U.S. Pat. No. 4,095,081, an annular 117 (FIG. 2) extending around the arcing zone through which secondary air is diverted from the air supply to the gun which also has primary atomizing air as described above in respect to U.S. Pat. No. 3,632,952. In addition an outlet nozzle 124 with two convergent passages 128 exiting in an axial plane with the primary air passage 120 receive air that also is diverted from the air supply. The convergent flow of air from the two passages 128 causes the spraying stream to be flattened, resulting in a fan-shaped spraying stream. Flow control is provided by a spring band 133 encircling the nozzle; the band is positionally adjusted to partially or completely close the convergent passages. There is otherwise no provision for interchanging between the annular and convergent flows or independently controlling these and the atomizing air.
U.S. Pat. No. 4,356,971 shows a gun similar to that described in U.S. Pat. No. 4,095,081 and additionally discloses a pair of supply conduits 18 (FIG. 3) connected to the gun, each of which supplies both electric power and air under pressure to the gun, the total amount of air being supplied from both conduits in sufficient quantity for the establishment of both the atomizing air and the operation of an air motor 42 (FIG. 2) to drive the wires. A manifold is utilized in which the air supplies from both conduits are combined prior to separation for delivery through separate passages to the air jet and the air motor drive.
It is also known to enclose a wire guide tube in a hose assembly that also provides air and power, as indicated in an advertising brochure entitled "Coaken Arc Spraying System" by Coaken Corporation, Japan, dated 1977.
A primary object of the present invention is to provide an arc spray system having an improved capability for modifying the spray of molten metal.
Another object of the invention is to provide an arc spray system having novel means for interchanging gas caps to modify the spray of molten metal.
Yet another object is to provide an improved, compact arc spray system having a capability for modifying the spray of molten metal.